The term "carcinoplacental isoenzyme" (CPI) refers to the appearance of a placental-type isoenzyme in cancer. This is analogous to the "carcinofetal" isoenzymes and proteins as they are all products of embryonic genes. As of now, the only well-established example of CPI is the Regan isoenzyme of alkaline phosphatase. The objective of this proposed research is to test the possibility that histaminase could be another CPI. This idea has resulted from reports in the literature and our observations that histaminase is produced at high levels by tumor cells, is closely correlated with Regan isoenzyme in its appearance, and from the fact that it is a placental enzyme (i.e., enriched in placenta but not in most of adult tissues). To achieve this goal, purification of histaminase from human placenta, kidney, small intestine and that produced by the tumor will be carried out. The molecular structure, physico-chemical and enzymatic properties as well as immunochemical characteristics of these enzymes will be compared to determine whether the enzyme produced by the tumor is identical to the placental enzyme. Furthermore, efforts will be made to develop sensitive and specific immunochemical methods for the measurement and detection of the "carcinoplacental histaminase". Proof that histaminase is a CPI would provide the indication that CPI is a characteristic of certain cancers, and thus contributes to a greater understanding of the basic biology of cancer. The establishment of another example of CPI would also be useful in the clinical evaluation of tumor progression and regression of tumor resulting from therapy.